First of all, the "3 Day Method" is a misnomer, kids get the "idea" in 3 days, they aren't trained in 3 days, the average is 3 to 6 months. Skittles and M&M's did zip for us, too, same with reward charts, stickers, toys...all a bust!! Kids aren't all the same, I don't know why we think everything that worked for others will work for every child, though it would be nice :-/
What DID work when he refused to poop was a "power incentive," something special to your own child, that you retain ownership of and the child "earns" the privilege of using it 30-60 minutes. This works with peeing or pooping refusal, and the site gives tips to help with children who will not sit on the potty like your daughter.
http://www.rogerknapp.com/medical/pottytrainingrefusals.htm
MANY children are afraid of the potty and toilet, for various reasons. You said yourself she isn't ready mentally, so you need to back off. Leave the potty out and tell her it's there if she wants to use it, put her back in diapers or training pants with covers and tell her the big girl panties are for when she uses the potty. Take her in the bathroom when you go so she can see it's a normal thing everyone does, but don't force her to go, just have her there and explain what you're doing so she learns how to wipe, flush, and wash her hands.
The fact that she will have a new sibling very soon (congrats!) means she will likely regress some anyway, a little or completely, so training now is probably fruitless and you would have to go down this road later anyway. My guy trained at 27 months, and just turned 3, but when I registered him for preschool for this September as well they told me if he wasn't potty trained the teacher would work with him, maybe that's the same where she'll be going? If so let her follow THEIR lead, then do the same at home, many times it works out better that way, especially since she'll see others her age doing the same thing. Something will just "click," she'll want to do what everyone else is and do it : )